1. Field of the Invention
The present invention relates to rotary servovalves, and in particular to high speed rotory servovalves, used to control the flow of fluids under high-pressure, particularly liquids.
2. Description of the Prior Art
Many different mechanical and electrical servovalve systems have been employed for controlling fluid flow in industrial and manufacturing environments, as well as in other applications. Fluid servovalve control systems which require precise and highly responsive control are employed in a multitude of widely varying applications, including the control of robots, the operations of presses for manufacturing rubber and plastic parts, the control of tensioning devices in the paper industry, automotive vehicle and parts manufacturing, petroleum refining operations, and numerous other applications.
In many of the applications in which servo control valve systems are utilized, pressurized fluid is typically provided from a high pressure source and transmitted through a load from which the fluid is then exhausted to a low pressure reservoir. The load may, for example, take the form of a double-acting piston operating within a cylinder. The transfer of fluid from one side of the piston to the other within the cylinder causes the piston to move some mechanism to which it is connected.
In a conventional rotary servovalve for the control of fluid flow, the fluid enters the valve housing at a single inlet port, and exits the valve housing to the load through a single first fluid transfer control port. Fluid from the load reenters the valve housing through a single second fluid transfer control port and exits the valve housing from a single outlet port. Flow through the valve is controlled by the position of the movable valve element which directs flow from the inlet port to the alternative fluid transfer control ports. The flow to the outlet port of the valve housing is to a fluid reservoir, which is maintained at a reduced pressure from the pressure of the fluid source. Consequently, the pressure within the flow passage through the valve leading from the high pressure fluid source is greater than pressure within the flow passage in the valve leading to the fluid reservoir.
Since the fluid flow passageway within the valve which conducts fluid from the high pressure fluid source is typically located on the opposite side of the valve from the fluid passageway that conducts fluid to the fluid reservoir, there is an imbalance in internal pressure within a conventional rotary fluid valve. The high pressure imbalance within the valve produces a bending moment on the movable valve element that must be overcome in order to rotate the valve element. As the requirement for torque to overcome this bending load increases, so does the mass of the components of the driving motor or rotary solenoid required to drive the servovalve in rotation.
Force balancing becomes significant and necessary when large operating supply pressures, for example on the order of 5000 psi, are used. Forces of this magnitude often exist in high-pressure hydraulic applications. With a conventional rotary valve, an extremely large, high inertia rotary solenoid is needed to overcome the unbalanced forces that occur. This results in a slower response and a need for greater operating energy in the solenoid actuator for the solenoid operated rotary valve.
The present invention is a servovalve upon which the fluid forces are balanced due to the port arrangements with which the valve is constructed. In a conventional rotary servovalve having a single radial inlet port in the valve housing, the high pressure of fluid entering the port acts on the rotatable member within the valve housing to press it against the opposite wall of the valve housing. This force imbalance creates a greater friction within the valve and necessitates the use of a higher torque motor than would otherwise be necessary to operate the valve if the valve were properly balanced.
In the present invention the force imbalance within the valve is virtually eliminated. This is achieved by providing the valve housing with at least a pair of inlet ports and at least a pair of outlet ports. At least two of the inlet ports are located on opposite sides of the valve housing angularly displaced one hundred eighty degrees from each other. Similarly, at least two of the outlet ports are located on opposite sides of the valve housing angularly displaced one hundred eighty degrees from each other. By necessity, the inlet valve ports must be longitudinally offset from each other and the outlet valve ports must be longitudinally offset from each other so as not to interfere with the other ports in the valve. Corresponding sets of first and second fluid control ports are likewise provided in the valve housing. At least two of the fluid control ports within each set are similarly angularly displaced one hundred eighty degrees from each other and are longitudinally offset from each other in the valve housing.
In a valve in which the valve housing has a pair of inlet ports and a pair of outlet ports, the rotary element of the valve is likewise provided with a pair of flow channels or passageways for connecting each set of valve ports. The flow channels in each pair of flow channels are laterally spaced from each other and the pairs of flow channels are longitudinally offset from each other on the movable valve element. As a consequence, pairs of flow channels are defined in which the flow channels in each pair conduct fluid through the valve in opposite directions from each other. Therefore, the forces within the valve are balanced, regardless of the direction of fluid flow, the extent to which the ports are open, and even under no flow conditions. As a result, less torque and, therefore, less massive components in the rotary solenoid are required in order to operate the rotary valve.
By reducing the mass of the rotary solenoid components, the inertia of the rotary solenoid is also reduced. Reduction in valve inertia results in an increase in the frequency bandwidth of responsiveness of the rotary solenoid to electrical input signals. An increase in frequency bandwidth produces a much faster response time of the rotary solenoid, and hence the servovalve, to electrical input signals that operate the solenoid.
In a preferred embodiment of the present invention the rotary servovalve is also balanced not only with respect to forces acting laterally in planes perpendicular to the valve axis, but also with respect to forces acting in planes passing through and containing the valve axis. This eliminates unbalanced forces that otherwise act evenly along the length of the rotatable valve element to exert a moment of torque that would tend to push one end of the rotatable valve element against one wall of the housing and the opposite end of the valve element along a diametrically opposite wall of the housing. Longitudinal torque imbalance along the length of the valve is avoided by providing sets of inlet and outlet ports in the valve housing and corresponding passageways through the rotatable valve element on diametrically opposite sides thereof.
To alleviate the rotational moments produced by rotational forces acting on the rotatable valve element of the invention even when the lateral forces are balanced, a valve configuration is adopted which achieves both lateral and longitudinal rotational force balancing. This is accomplished by providing a pair of diametrically opposed central valve ports each having a cross-sectional area twice that of the area of each opening in upper and lower sets of valve ports. The areas of the upper and lower valve ports are equal to each other. Also, the upper and lower valve ports are spaced equal distances from the central valve ports.
In one broad aspect the present invention may be defined as an improvement in a rotary servovalve system in which fluid is directed through an inlet port, an outlet port, a first fluid control port, and a second fluid control port in a valve housing as directed by a movable valve gate element. The valve gate element is rotatable within a housing in opposite directions of angular rotation from a position prohibiting fluid flow through any of the ports to alternative positions permitting fluid flow in alternative opposite directions through each of the first and second fluid control ports. According to the improvement of the invention a plurality of each of the foregoing ports are provided. At least two of each of the different types of ports are located on opposite sides of the valve housing from each other. The ports are located in the valve housing so offsetting longitudinal bending forces on the movable valve element are created by fluid pressure within the valve.
In a preferred embodiment the invention may be considered to be an improvement in a rotary valve including a hollow cylindrical housing defining a longitudinal axis and having inlet and outlet ports and defined therethrough, and a valve core of cylindrical configuration having transverse passageways defined therethrough and rotatably mounted within the valve housing. According to the improvement of the invention the ports are aligned on the valve housing and the passageways are alignable with the ports by rotation of the valve core within the housing so that rotational bending moments upon the valve core produced by fluid pressure in the passageways are balanced at all times.
In a further preferred rotary valve according to the invention the valve housing and the valve core both have first and second ends and the ports are comprised of a first end inlet port, a second end inlet port, a central inlet port, a first end outlet port, a second end outlet port, and a central outlet port. The end inlet and outlet ports are each equal in area to each other and are each half the area of each of the central ports. The first end inlet port, the central outlet port and the second end inlet port are angularly aligned with each other and the central outlet port lies midway between the end inlet ports in a longitudinal direction. The first end outlet port, the central inlet port and the second end outlet port are angularly aligned with each other, and the central inlet port lies midway between the end outlet ports. The first and second end inlet ports are angularly displaced 180 degrees from the first and second end outlet ports and the central inlet port is angularly displaced 180 degrees from the central outlet port. Preferably, the first and second end inlet ports are respectively located diametrically opposite the first and second end outlet ports. Preferably also, the ports are rectangular in cross-section and are equal in angular width.